In the market, there are many kinds of locks. Since the quincunx-shaped lock has a special design offering a wide variation, it is usually used on motor-cycles, travel cases, alarm devices, the code control of electric apparatus, doors, cases, windows, and the like. In the said lock, an upper lock pin is provided on the upper pin seat, and a lower lock pin on the lower pin seat; by means of the key, the upper lock pins push the lower lock pins so as to turn the upper pin seat to unlock the lock. Unfortunately, a skilled locksmith or person will be able to unlock it by using a special tool to adjust the upper and lower lock pins to a correct position. In the present invention, the structure and the shape of the lower pin seat and the lower lock pins are specially designed to have the lower lock pins move in a longer space so as to make it impossible for a burglar to unlock it without the correct key because the lower lock pins cannot be adjusted to the correct position.